Is higher voltage always better when stringing PV modules?

The principle for selecting the voltage of PV module strings is not simply to pursue the highest possible voltage. The key is to achieve a precise match with the rated input parameters of the inverter, while comprehensively considering system safety, power generation efficiency, and overall cost, ultimately achieving a multi-dimensional balance and optimization.

Excessive voltage poses two core risks: First, it can easily exceed the inverter's maximum DC input voltage threshold, directly triggering the inverter's overvoltage protection mechanism and causing shutdown and power interruption. In extreme cases, it may also damage the inverter's internal power devices, creating safety hazards and increasing subsequent maintenance costs. It's particularly important to note that the open-circuit voltage of photovoltaic modules increases with decreasing temperature; typically, for every 1°C drop in temperature, the open-circuit voltage increases by 0.3% to 0.4%. Therefore, voltage peaks in low-temperature winter environments must be a critical consideration in string design to ensure that the voltage remains within the inverter's safe operating range. Second, higher voltages also place higher demands on the voltage withstand rating of system hardware. Components such as module junction boxes, cable insulation, and connectors require products with higher voltage withstand standards, directly increasing hardware procurement costs. Furthermore, during installation and maintenance, high-voltage environments increase the risk of electric shock, necessitating more stringent insulation protection measures.

Conversely, excessively low voltage also has negative impacts: In terms of power generation efficiency, if the string voltage is lower than the inverter's minimum operating voltage (MPPT), the inverter will be unable to stably track the maximum power point, leading to a significant drop in power generation efficiency. Furthermore, under the same power output scenario, lower voltage results in higher loop current. According to the power loss formula P=I²R, cable power loss will increase significantly, causing unnecessary power waste. In terms of system configuration, low voltage means a reduction in the number of modules per string. To meet the overall system's power requirements, the number of strings must be increased, further increasing the number of inverter connections. This not only drives up equipment procurement costs but also complicates system wiring.

The rational design of string voltage needs to follow a clear core logic: the key is to accurately match inverter parameters. When calculating the number of modules per string, two core conditions must be met simultaneously: the open-circuit voltage of the modules in low winter temperatures must not exceed the inverter's maximum DC input voltage, and the operating voltage of the modules in high summer temperatures must not be lower than the inverter's minimum MPPT voltage. Based on this, it is also necessary to balance cost and efficiency. Within the voltage range allowed by the inverter, the configuration scheme that is close to the median of the MPPT voltage range should be selected first. This can effectively reduce the loss caused by loop current and ensure that the inverter can maintain a stable maximum power point tracking efficiency under different operating conditions. This is the most cost-effective choice.